The use of electrical stimulation to modify neural activity is both an old and an extensive field of scientific, engineering, and clinical activity. Historically, the parameters for the stimulation, including the locations of the electrodes used to apply the stimulation, were determined by trial and error. In many cases, this approach is still used today.
Although electrical stimulation of sufficient strength normally produces a physiological response, the responses are not always consistent or repeatable between practitioners. With the goal of explaining/understanding this variability, efforts have been made to analyze/predict the response of neural tissues to electrical stimulation from an electromagnetic field theory point of view.
As a result of these efforts, the present state of the art uses a combination of (1) tissue geometry and electrical properties obtained from, for example, CT and MRI images including diffusion tensor magnetic resonance images, and (2) electric field distributions and their associated current density distributions obtained from computer simulations. Based on these inputs, clinicians and researchers have become better able to select stimulation parameters, including electrode locations, for invasive procedures that use electrodes within the body (e.g., deep brain and spinal cord stimulation), non-invasive procedures that use electrodes located on the surface of the body (e.g., transcranial brain stimulation, transcutaneous spinal cord stimulation, and transcutaneous peripheral nerve stimulation), and systems that use combinations of internal and surface electrodes.
Examples of the broad range of electrical stimulation protocols and techniques that have been the subject of patents and patent applications include: U.S. Pat. No. 9,339,642 assigned to Soterix Medical, Inc., and entitled “System and Method for Conducting Multi-Electrode Electrical Stimulation;” U.S. Pat. No. 9,327,119 assigned to Vision Quest Industries Incorporated and entitled “Electrostimulation System;” U.S. Pat. No. 9,302,107 assigned to Second Sight Medical Products, Inc., and entitled “Cortical visual prosthesis;” U.S. Pat. No. 8,914,122 assigned to Electrocore, LLC, and entitled “Devices and Methods for Non-Invasive Capacitive Electrical Stimulation and their Use for Vagus Nerve Stimulation on the Neck of a Patient” U.S. Pat. No. 8,903,494 assigned to Thync, inc., and entitled “Wearable Transdermal Electrical Stimulation Devices and Methods of Using Them;” U.S. Pat. No. 8,818,515 assigned to the City University of New York and entitled “Voltage Limited Neurostimulation;” U.S. Pat. No. 7,684,866 assigned to Advanced Neuromodulation Systems, Inc., and entitled “Apparatus and Methods for Applying Neural Stimulation to a Patient” U.S. Pat. No. 7,340,299 assigned to Emory University and entitled “Methods of Indirectly Stimulating the Vagus Nerve to Achieve Controlled Asystole;” U.S. Patent Application Publication No. 2016/0055304 assigned to Aaken Laboratories and entitled “Targeted Electrical Stimulation;” U.S. Patent Application Publication No. 2015/0174418 assigned to Thync, inc., and entitled “Device and Methods for Noninvasive Neuromodulation Using Targeted Transcranial Electrical Stimulation;” and U.S. Patent Application Publication No. US 2015/0112403 assigned to Neuroelectrics Barcelona S. L. and entitled “Method and a System for Optimizing the Configuration of Multisite Transcranial Current Stimulation and a Computer-Readable Medium.” The recent text The Stimulated Brain: Cognitive Enhancement Using Non-Invasive Brain Stimulation, Academic Press, London, U K, 2014, edited by Roi Cohen Kadosh (hereinafter the “Kadosh text”), discusses the extensive scientific literature regarding the use of non-invasive electrical stimulation to modulate brain activity, including the use of computer modeling in this effort (see, in particular, Chapters 2 and 4, of the Kadosh text; Kindle Locations 1221-1897 and 2630-3326). The contents of the foregoing references, as well as those cited below in this section and in the Detailed Description, are hereby incorporated herein by reference in their entireties as examples of the existing state of the art. The references are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence or paragraph in which the reference is cited.
The standard method for performing computer simulations used in selecting stimulation parameters is the finite element method (FEM) for which both open source and commercial software packages are available, e.g., the COMSOL Multiphysics Finite Element Analysis Software (previously FEMLAB) distributed by COMSOL, Inc., Burlington, Mass. See, for example, U.S. Pat. No. 8,180,601 assigned to the Cleveland Clinic Foundation and entitled “Systems and Methods for Determining Volume of Activation for Deep Brain Stimulation.” The output provided to the clinician or researcher is often a pseudocolor image of the neural tissue, e.g., the brain, showing distributions of electric fields and/or their associated current densities within the tissue. The clinician or researcher can adjust stimulation parameters (e.g., by moving electrodes, selecting electrodes from a set of electrodes, and/or changing electrode montages) and examine the effects of the adjustments on the field/current distributions. In this way, the computer simulations become part of the ultimate decision on the stimulation protocol used to modify neural activity.